//MainActivity
public class MainActivity extends Activity {
    static {
        System.loadLibrary("native-lib");
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView tv = (TextView) findViewById(R.id.sample_text);
        tv.setText(stringFromJNI());
    }
    public native String stringFromJNI(String param);
}
//native-lib.cpp
#include <jni.h>
#include <string>
extern "C" JNIEXPORT jstring JNICALL
Java_com_hook_yocn_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

//MainActivity.java
public class MainActivity extends Activity {
    static {
        System.loadLibrary("native-lib");
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView tv = (TextView) findViewById(R.id.sample_text);
        tv.setText(stringFromJNI("java"));
    }
    public native String stringFromJNI(String param);
}
//native-lib.cpp
#include <jni.h>
#include <string>
#include <android/log.h>
#define LOG_TAG "hook"
#define LOGV(...)  __android_log_print(ANDROID_LOG_VERBOSE,LOG_TAG,__VA_ARGS__)
#define LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)
extern "C" JNIEXPORT jstring JNICALL
Java_com_hook_yocn_MainActivity_stringFromJNI(JNIEnv *env, jobject obj, jstring param) {
    int length = (env)->GetStringLength(param);
    const char *nativeString = (env)->GetStringUTFChars(param, 0);
    char *resultChars = new char[length + 1];
    for (int i = 0; i < length; ++i) {
        resultChars[i] = nativeString[i] + 1;
    }
    resultChars[length] = '\0';
    std::string par = resultChars;
    LOGE("輸入?yún)?shù)->%s,長(zhǎng)度:%d", nativeString, length);
    LOGE("輸出結(jié)果->%s", resultChars);
    return env->NewStringUTF(resultChars);
}

// 我們自己的libhook.so push到內(nèi)存卡并且重命名為libnative-lib.so
adb push libhook.so /mnt/sdcard/libnative-lib.so
// 進(jìn)到手機(jī)目錄
adb shell
// 獲取root權(quán)限
su
// 到so存放目錄
cd /data/data/com.ahook.yocn/lib
// 宿主的so拷貝一份，因?yàn)槲覀冞€要調(diào)用，起個(gè)別名，我們還要用
cp libnative-lib.so libnative-lib-src.so
// 將我們push進(jìn)來(lái)的so拷貝到當(dāng)前目錄并覆蓋宿主apk的so
cp /mnt/sdcard/libnative-lib.so .

2019-07-06 21:49:45.531 12052-12052/com.ahook.yocn E/com.ahook.yocn: No implementation found for java.lang.String com.hook.yocn.MainActivity.stringFromJNI(java.lang.String) (tried Java_com_hook_yocn_MainActivity_stringFromJNI and Java_com_hook_yocn_MainActivity_stringFromJNI__Ljava_lang_String_2)
2019-07-06 21:49:45.533 12052-12052/com.ahook.yocn E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.ahook.yocn, PID: 12052
    java.lang.UnsatisfiedLinkError: No implementation found for java.lang.String com.hook.yocn.MainActivity.stringFromJNI(java.lang.String) (tried Java_com_hook_yocn_MainActivity_stringFromJNI and Java_com_hook_yocn_MainActivity_stringFromJNI__Ljava_lang_String_2)
        at com.hook.yocn.MainActivity.stringFromJNI(Native Method)
        at com.hook.yocn.MainActivity.onCreate(MainActivity.java:21)
 ......

// hook.cpp
#include <jni.h>
#include <string.h>
#include <vector>
#include <stdio.h>
#include <android/log.h>
#include <android/bitmap.h>
#include <unistd.h>
#include <sys/stat.h>
#include <string>
#define LOG_TAG "hook"
#define LOGV(...)  __android_log_print(ANDROID_LOG_VERBOSE,LOG_TAG,__VA_ARGS__)
#define LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)
using namespace std;
extern "C" {
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
//宿主動(dòng)態(tài)鏈接庫(kù)路徑
#define LIB_CACULATE_PATH "/data/data/com.ahook.yocn/lib/libnative-lib-src.so"
//函數(shù)指針
typedef jstring (*CAC_FUNC)(JNIEnv *env, jobject thiz, jstring param);
jstring callFunc(JNIEnv *env, jobject thiz, jstring param) {
    void *handle;
    char *error;
    CAC_FUNC cac_func = NULL;
    //打開(kāi)動(dòng)態(tài)鏈接庫(kù)
    handle = dlopen(LIB_CACULATE_PATH, RTLD_LAZY);
    if (!handle) {
        LOGV("dlopen: %s\n", dlerror());
    }
    //清除之前存在的錯(cuò)誤
    dlerror();
    //獲取一個(gè)函數(shù)
    *(void **) (&cac_func) = dlsym(handle, "Java_com_hook_yocn_MainActivity_stringFromJNI");
    if ((error = const_cast<char *>(dlerror())) != NULL) {
        LOGV("dlsym: %s\n", error);
    }
    jstring ret = (*cac_func)(env, thiz, param);
//    printfJstring(env, thiz, ret);
    //關(guān)閉動(dòng)態(tài)鏈接庫(kù)
//    dlclose(handle);
    return ret;
}
JNIEXPORT jstring JNICALL
Java_com_hook_yocn_MainActivity_stringFromJNI(JNIEnv *env, jobject thiz, jstring param) {
    LOGE("Java_com_hook_yocn_MainActivity_stringFromJNI");
    string hookPre = "Hook_Head ";
    string paramString = (env)->GetStringUTFChars(param, 0) + hookPre;
    string modifyString = hookPre + paramString;
    jstring modifyParam = env->NewStringUTF(modifyString.c_str());
    jstring ss = callFunc(env, thiz, modifyParam);
    string rawResult = (env)->GetStringUTFChars(ss, 0);
    string hookEndString = rawResult + " Hook_End";
    return env->NewStringUTF(hookEndString.c_str());
}
} //extern "C"
//Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_LDLIBS    := -llog -ljnigraphics
LOCAL_MODULE    := hook
APP_PROJECT_PATH:= LOCAL_PATH
LOCAL_SRC_FILES := hook.cpp
LOCAL_CFLAGS    =  -ffast-math -O3 -funroll-loops
include $(BUILD_SHARED_LIBRARY)
//Application.mk
APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions
APP_ABI := x86
APP_PLATFORM := android-28

adb push libhook.so /mnt/sdcard/libnative-lib.so
...